Apparatus or guns of this kind are generally used for the application of sealants for thermal and/or sound insulation.
The base wall of a cartridge is intended to slide as a result of the feed of a piston actuated manually with the aid of a pump lever by means of a rack and pinion or friction feed mechanism.
One known mechanism with a friction feed rod--U.S. Pat. No. 4,840,294--includes a front feed sprocket and a rear non-return sprocket mounted on the rod, each extending in a plane substantially perpendicular to the latter.
The feed sprocket is intended to engage the piston rod by movably pivoting over the rod as a result of the pumping of the lever in order to drive the piston towards the front in an elementary feed motion and to disengage the non-return sprocket already engaging the rod after completion of a pumping operation so as to, thereby block the piston in order to prevent it from moving backwards.
The application of a predetermined quantity of the product from the cartridge requires a certain feed of the piston resulting from a plurality of successive pumping operations.
In short, using an apparatus of this kind, an operator must tire himself out pumping a great many times in order to apply his product.